Monday, January 31, 2011

The SPC is forecasting a slight risk of severe thunderstorms for portions of Texas overnight and early Tuesday, ahead of the major winter storm we've been talking about for the past few days.

NWS doppler radar near Abilene currently shows thunderstorms erupting along and immediately West of the cold front across Northwest Texas:

As the evening wears on, increasing upper-level energy will overspread the region from the West, while at the same time the surface cold front will be diving to the Southeast. This will result in increasing thunderstorm activity across the Hill Country and adjacent areas.

When the heart of the upper-level energy nears the frontal boundary and increasing low-level moisture later tonight, some thunderstorms may produce gusty winds and hail to severe limits across portions of central and southcentral Texas during the predawn hours on Tuesday.

I apologize for not getting an update out earlier today. My 'real job' simply prevented me from doing so. Sometimes the juxtaposition of a Monday with a major impending storm just doesn't work out...

In general, the major impact areas outlined in yesterday's post are still right on target. I did, however, increase the heavier snowfall accumulation amounts further southwest across Oklahoma based on continued computer model guidance and the anticipated track of the system.

With the above in mind, here is how it appears to me that the heavier snow fall totals will play out through Tuesday night:

While the magnitude of the potential snowfall amounts alone is significant, I would encourage residents of the region to not just focus on the snowfall accumulation forecasts. What will make things even worse are strong North to Northeast winds of 20-30 mph with gusts to 40 mph or higher, which will cause widespread blowing and drifting snow. Blizzard to near blizzard conditions can be expected throughout much of the region highlighted with 8-12 inch plus snowfall totals. This will cause widespread drifting of snow, in addition to very dangerous wind chill readings.

Across Oklahoma and Missouri, snow may fall at a rate of 2-3 inches per hour in some cases, accompanied by rumbles of thunder and flashes of lightning.

Ice will also be a threat for portions of the region immediately Southeast of the heavy snow band. The primary threat area for greater than one-quarter of an inch of ice accumulation is outlined below:

Some initial icing (but generally less than one quarter of an inch) may also take place across portions of Oklahoma, southeast Kansas and southwest Missouri prior to the complete changeover to snow, which will further aggravate already hazardous conditions across the region.

The above scenarios are what are most likely to play out as the system develops tonight and Tuesday. There are, of course, more extreme versions of what could take place. One computer forecast model, for example, is calling for 20-24" of snow in band generally extending from the Tulsa, Oklahoma area, through Joplin and Springfield to near St. Louis, Missouri. The axis of heaviest snow from northeast Oklahoma through southwest and into east-central Missouri seems likely to me. We'll have to wait to see how the hourly snowfall rates start playing out to see if some of the more the extreme accumulations also come to pass.

Finally, below is a snapshot of the current winter weather warnings from the National Weather Service:

The pink shaded region from northwest Texas and the panhandle, Northeast through the Midwest and into New England indicates a Winter Storm Warning. The brighter orange shaded areas from central Oklahoma through Missouri and parts of Iowa and Illinois are Blizzard Warnings. Much of these areas are surrounded by Winter Weather Advisories, noted by the blue/grey shaded areas.

Residents in the warned areas should have already completed necessary preparations for this dangerous storm. Listen to local media and other outlets for later statements, warnings and advisories.

I will make every effort to provide some real-time update posts on Tuesday, but please remember this blog is not meant for real-time information on a consistent basis. For that, please consult your local media and/or National Weather Service office. A map of local offices can be found here.

Sunday, January 30, 2011

A major winter storm will impact a large part of the nation this week. This particular post focuses on the period Tuesday through Wednesday.

A strong upper level low pressure system was moving onshore in the extreme Northwest part of California this afternoon:

This system will drop southeast along the Arizona/New Mexico/Mexico borders through Monday:

then lift back Northeast into the southern and central Plains Monday night into Tuesday:

This system, in combination with a surge of cold, arctic air from Canada, will produce widespread, wintry precipitation in a large area from the central and southern Plains into the Midwest and Ohio Valley Tuesday and Wednesday:

Within the larger overall winter outlook region, locally significant amounts of snow and/or ice are forecast for many areas.

Within the red shaded areas on the map above, one quarter to one half inch of ice accumulation is likely, with locally heavier amounts possible. (The integrity of trees and power lines comes into question with one quarter inch of ice or more). In addition, strong & gusty North to Northeast winds of 30-40 mph with gusts to 50 mph will create further problems. Significant power outages can be expected in these areas.

Locally heavy snow may also fall over parts of the ice storm regions during the last 12 hours of the event (see outlook and maps below). This would obviously further aggravate an already very hazardous situation in these areas.

Heavy snow will be widespread from portions of central and northern Oklahoma into east-central Kansas, northern Missouri (including the Kansas City metro area) into northern Illinois (including the Chicago metro area) and extreme northern Indiana and southern Michigan:

Snowfall totals of 6 inches (with locally heavier amounts) will be widespread within the area outlined in the lighter blue shading on the map above (including the Oklahoma City & Tulsa metro areas). Widespread amounts of 10-15 inches, with locally heavier amounts, are likely within the darker blue outline (including eastern parts of Kansas City and all of the Chicago area). One computer model is currently forecasting a "bullseye" of 15-20 inch snowfall totals for the greater Chicago area by 6am Wednesday morning.

In addition to the heavy snow, widespread winds of 30-40 mph with gusts to 50 mph will create blowing and drifting snow. Blizzard to near blizzard conditions can be expected for much of the areas outlined above.

Surrounding the 6 inch plus snowfall area, a large area of 3-6 inch snow will cover the Plains from the Texas panhandle and western Oklahoma into much of Kansas and adjacent portions of Nebraska and Iowa.

Currently, the National Weather Service has Winter Storm Watches (blue/grey shading) and/or Blizzard Watches (lime green shading) already in effect for much of the regions outlined above, valid late Monday or early Tuesday through Wednesday:

It's still relatively early in the game for this system, however the above should give you a good idea as to how the event is expected to unfold. Residents of the central and southern Plains into the Midwest and Ohio Valley should prepare now for the approaching winter storm. Listen to local media for the latest updated forecasts, watches and warnings for your area.

This will be a 2 part post, first dealing with the arctic air that will invade the nation over the next few days. The 2nd will deal with the precipitation aspects of the impending winter storm...

Below is the HPC surface forecast map valid 6pm CST Monday evening:

Note the leading edge of cold, arctic air spreading southward through the central and northern Plains. The center of the high pressure system associated with the arctic blast is noted by the "H", located just north of the Montana border with Canada.

By 6am CST Tuesday morning, just 12 hours later, the front will have blasted south into Texas, with cold air spilling in behind. High temperatures across the Lone Star State will occur in the early morning hours Tuesday, with temperatures falling throughout the day:

By 6am CST Wednesday, the front will have advanced through much of the deep south and into the Gulf of Mexico:

Cold air will continue spilling south behind the front, with readings across most of Texas not expected to leave the 30s:

GFS Model Forecast Surface Temps valid 6pm CST Weds 2-2-11

Strong and gusty North winds behind the front will produce dangerous wind chills across the Plains and Midwest both Tuesday and Wednesday.

My next post will touch on the precipitation potential with this system...and it looks like it will be a doosy for much of the Plains & Midwest! Stay tuned!

The blue/grey shaded region from Oklahoma through the Midwest indicates a Winter Storm Watch that has been posted, generally valid from Monday evening in the Southwest through Wednesday night in the Northeast portions of the watch area.

I am going to take a look at the full morning computer forecast model suites before making any specific predictions, but in general, a heavy snow event appears likely from portions of east-central Kansas to northern Illinois. A significant ice event is possible just south of the heavy snow axis, from portions of northeast Oklahoma and southeast Kansas, through southern and central Missouri into central and southern Illinois.

Meanwhile, a major arctic cold blast will impact the central and southern Plains and Midwest late Monday into Tuesday.

I'll make a more detailed posting later this morning or early this afternoon, after examining all of the latest data.

Saturday, January 29, 2011

The above map from the SPC in Norman, OK shows a "slight" risk of severe weather for much of southcentral and southeast Texas overnight tonight.

In meteorology this is what we call a "conditional" risk of severe weather. By that I mean that it is uncertain that thunderstorms will develop, but if they do then they are likely to become strong to severe.

A strong upper-level weather disturbance, currently lifting Northeast across Mexico, will move across the region overnight. Southerly winds have brought an increasingly moist airmass Northward across Texas today, and this moisture will interact with the disturbance to produce widespread showers across the region overnight and early Sunday morning.

A few thunderstorms could also develop overnight, and if so, are likely to produce hail to severe limits. Gusty winds are also possible.

At this time, it appears that the best chance of thunderstorm development will take place after 3 a.m. central time, into the early morning hours on Sunday.

Friday, January 28, 2011

I'm not at the computer where I can illustrate images this morning, so the static HPC forecast maps below will have to do for now (I'll provide a more detailed post later today or tomorrow morning). First is the surface map with frontal positions valid Tuesday morning at 6am CST:

As you can see, the front will be blasting southward into the southern Plains at that time. Temperatures will be falling throughout the day across most of Texas, and a band of wintry precipitation is likely from Oklahoma and Kansas into Missouri.

By 6am CST Wednesday, the arctic front will have progressed across much of the deep South into the Gulf of Mexico. Wintry precipitation will likely be taking place from eastern Missouri into the Ohio and portions of the Tennesee Valleys.

I'll provide a more detailed post, specifically with regard to precipitation potential with this system, later today and/or Saturday morning.

Wednesday, January 26, 2011

If you live in the NYC metro area and love snow, it's been an awesome winter. If you hate it, you're undoubtedly miserable. Yet another major snowstorm is underway across the Northeast this evening. Below is the latest radar image from the New York City area radar (located approximately in the center of the screen):

At 6pm CST (7pm EST), freezing drizzle was reported at both Laguardia and Central Park. Sleet was reported at JFK.

A mixture of freezing rain, sleet and snow is likely to continue in NYC this evening, before changing over to mostly snow overnight. At this time, from 8 to 12 inches of snow is forecast across much of the region overnight:

The heaviest snows may fall over portions of central and western New Jersey:

Winter storm warnings are in effect for much of the Northeast through tonight:

In a post yesterday, we pointed out that severe weather was likely across much of the Florida peninsula, including a risk of tornadoes. Below is a map (click to enlarge) of observed severe weather reports from across the "sunshine state" yesterday:

As you can see, severe wind reports were widespread across the middle third of the peninsula, with several tornado reports as well. (Note the expanded text boxes on the left side of the image for additional details on the tornado reports).

Fortunately, it appears that there were no serious injuries or deaths associated with the system.

Tuesday, January 25, 2011

A somewhat complex surface weather pattern will result in one to possibly two rounds of severe weather across much of the Florida peninsula today. The above surface weather map is valid at 6pm CST (7pm EST) today. The map below shows the severe weather risk area as outlined by the Storm Prediction Center (SPC) for this afternoon and tonight:

The greatest severe weather potential, including a chance of tornadoes, is likely to take place along and south of a warm front that is expected to lift from Southwest to Northeast across the state late this afternoon into this evening.

Another round of severe storms is then possible tonight as a cold front sweeps across the state from the West.

Residents of Florida, particularly South of a Jacksonville to Apalachicola line, should remain alert today and listen for later updates, watches and warnings.

The northern part of Minnesota is often affectionately referred to as the "icebox of the nation". As you can see by the above forecast high temperature map for today, they have certainly earned that distinction.

Yes, you're reading the map right: -3 for a high in Grand Rapids, -2 in Hibbing, and a balmy -5 at International Falls.

The low temperature this morning in International Falls was -26. It has since warmed to a balmy -18 as of 8am CST. Good to see that they are well on their way to that -5 high for this afternoon!

Thursday, January 20, 2011

In a post last night, I remarked that a 2-4 inch snow event appeared likely across northern portions of Oklahoma and Arkansas today.

Below is a snapshot of snow reports across the region today (click to enlarge):

I've highlighted some of the heavier amounts in the more heavily populated areas in the blue text boxes.

As you can see, a widespread swath of 2-4 inch snowfall took place from near Woodward in northwest Oklahoma, through the Bentonville and Rogers areas in northwest Arkansas.

Across the Tulsa metropolitan area, 2-4 inch reports were widespread, with heaviest amounts on the north side of the area (click to enlarge):

Please note that within the blue text boxes, "Event: 3 Snow" means that 3 inches of snow was measured at that location.

Below is what a computer forecast model was calling for (yesterday evening) as far as snowfall totals are concerned. As you can see, this particular model did a very good job in not only estimating the location but also the intensity of the event:

I don't have many childhood memories of "significant" snow events in my hometown of Tulsa, OK. It seems like ever since I moved from there (about 25 years ago) I hear of them frequently, wouldn't you know it!

"Significant", of course, is a relative term. When you're from Oklahoma (at least most of the state), 2 or 3 inches are "significant" in most people's book (including mine). Heck, now that I live in southcentral Texas, 1 inch would be considered a downright blizzard (as long as the wind was blowing at 5 mph or more).

My family and friends up in the Tulsa area are in for a snow event tomorrow. Whether or not it will be a "significant" event probably depends on who you talk to. If I were living there, I'd call it significant, as 2-4 inches seem likely. If my cousin from from Michigan were talking, he'd laugh in my face at such a notion.

The area of high pressure that you see over the northcentral Plains will surge southward tomorrow, being reinforced by a blast of arctic air from the North. Below is what the map will look like at 6am CST tomorrow morning:

At the same time, an upper level weather disturbance will approach the region from the West, producing uplift and a band of moderate to locally heavy snow across portions of northern Oklahoma. This heavier band of snow will eventually spread into portions of northern Arkansas.

Below is what one computer model is forecasting (as far as total snow accumulation is concerned) across the region for the period ending 6pm CST on Thursday evening:

You can also see that another band of moderate to heavy snow is forecast across northeast Kansas and parts of northwest and northcentral Missouri.

Meanwhile, down here in Texas, another "backward" day can be expected. Temperatures will be warmest in the morning, then hold steady or slowly fall during the afternoon as the cold front blasts through the state. Here is where the front is forecast to be located by 6pm CST Thursday evening:

...and you guessed it, South Texans, no snow (or anything remotely similar) is instore for us. The northcentral and northeast corner of the state may see a brief mixture of rain, sleet and snow Thursday morning, but significant accumulations are not expected.

Sunday, January 16, 2011

The above image was taken from the New Braunfels, TX doppler radar a few moments ago. It depicts the radar's estimate of storm total rainfall from the rain event we've had over the past 3 days.

If you believe the radar estimate, approximately 0.15 inch of rain fell at my home near Kyle, TX. In fact, my official CoCoRaHS rain gaugeshows that we've received 1.40 inches of rain since Friday.

What's the deal, you ask? While the WSR-88D (which is 1988 technology, mind you) does a good job of estimating convective (thunderstorm-related) and other heavy rainfall events, it doesn't always handle the lighter stuff all that well (i.e., pro-longed periods of light rain or drizzle over an extended period of time).

Scientists at the National Severe Storms Laboratory (NSSL) in Norman, OK (the weather and weather radar capital of the universe) are currently experimenting with a new type of radar, called Phased Array. Not only does that technology promise to improve precipitation estimates in all types of situations, but more importantly will likely lead to even earlier warning of severe and tornadic thunderstorms and other hazards.

Instead of sampling the atmosphere with one single radar beam every 4-7 minutes (as with the current radar system), phased array would sample the atmosphere every 20-30seconds, and using multiple beams that can be focused on one particular storm or part of a storm for extended evaluation.

Don't be alarmed, fellow residents of southcentral Texas. That yellowish orange ball that you see emerging on the Western skyline is in fact the sun (also known as "Ray" for those of you who follow Bear in the Big Blue House).

We are not under attack by alien beings...

Carry on...

(Disclaimer: For readers in other parts of the country and world, just so I may clarify so that you don't think I have lost my marbles; we haven't seen the sun in about 7 days here in southcentral Texas. I therefore made this post out of concern that some of my fellow Texans may be confused about and/or afraid of the emerging fireball that we are currently witnessing).

Friday, January 14, 2011

Chilly weather continues for the 6th day in a row across the Lone Star state (just as we expected 10 days ago), with highs struggling to get out of the 40s across most of the central and eastern two-thirds of the state again today.

Winds just above the surface have already turned out of the Southeast across most of the state, which is gradually bringing moisture back up from the Gulf of Mexico. As a result, areas of fog and drizzle can be expected today across particularly southcentral & southeast Texas. Some patches of light rain will also be possible by afternoon, but rainfall amounts today are expected to be light:

Rainfall rates and coverage will increase on Saturday, particularly across southcentral portions of the state, as an upper level weather disturbance slowly moves in from the West/Southwest:

This disturbance will cause rainfall coverage and rates to increase and spread into Northern and Eastern portions of the state on Sunday:

Tuesday, January 11, 2011

Somehow this little tidbit slipped under my radar (pun intended), but did you know that effective yesterday, the 'Tropical Prediction Center' officially changed it's name (back) to the 'National Hurricane Center'?

During the "modernization" frenzy of the 1990's, the National Weather Service changed the name of the "National Hurricane Center" (NHC) to the "Tropical Prediction Center" (TPC). The name never really took off. In fact, they left "National Hurricane Center" on the website and many products even after the original "name change" took place.

Anyway, I guess after pondering it for 15 or so years they decided to change the name back to the NHC.

I wish they'd do the same with the Storm Prediction Center (SPC). I liked its former name "National Severe Storms Forecast Center" (NSSFC) a lot better, but what do I know?

Sunday, January 9, 2011

Remember the New Year's Eve tornado near Byram, MS, a little more than a week ago? Well... right now in Byram, a mixture of sleet and snow is falling. See the Jackson, MS radar image above for the current winter weather. Below is an image from the same radar on New Year's Eve. What a contrast!

The above radar image was taken from the Little Rock radar a moment ago. It's standard reflectivity (precipitation) mode but I've enhanced the color table to be more sensitive to wintry precipitation (i.e., snow, sleet, freezing rain).

The bright white reflectivity over Dallas and Cleveland counties shows snowfall rates of 1-2 inches per hour. Indeed, surface reports within the last hour indicate 1 inch of snow on the ground near Rison (in Cleveland County), and still coming down at a moderate to heavy pace.

This activity will spread East-Northeast into adjacent portions of Mississippi as the afternoon and evening progress.

Below is the latest computer model forecast of snow depth at Midnight CST, later this evening/early Monday morning:

Keep in mind that by the valid time of the forecast image, the snow will have ended across Arkansas, and will be just about peaking over Mississippi.

The above image shows the radar's estimate of total rainfall overnight, from the New Braunfels, TX radar. The medium to darker green shadings show widespread 1 inch totals, with 1.5-2 inches in the brighter yellow and orange areas between Austin and Houston. The maximum estimate by the radar is 2.78 inches, over portions of Lee and Fayette Counties (about 70 miles Northwest of Houston).

Much needed rain indeed, and without any significant severe weather, which is a good thing since this took place during the overnight hours.

Widespread precipitation has exited all but the far eastern and northeastern counties of Texas as of this writing, but now is when the winter weather event will begin to unfold across the South.

Below are the latest HPC forecasts of snow greater than 4 inches and freezing rain (ice) accumulation of at least one-quarter inch for today and tonight:

I'll make a more detailed post on the unfolding winter weather event around midday, after taking a closer look at the morning computer model runs. Generally, it appears that our thinking from yesterday is still on track.

Saturday, January 8, 2011

The above image of the Laughlin AFB radar (located about 30 miles East of Del Rio, TX) was taken just a few moments ago. It shows the beginnings of the "Texas soaker", as rain is breaking out over Mexico, and moving Eastward.

Precipitation will continue to expand and intensify overnight as it moves Eastward into Texas, leading to widespread, much needed rain and thunderstorm activity across the region.

See my earlier post for more detailed information on what to expect from this system.